The present invention is concerned with production of ophthalmic lens elements composed of a cured organic monomer formulation. The element may be an all-plastic lens cast from a thermosetting formulation, such as an epoxide, or the widely used allylic carbonate available from PPG Industries, Pittsburgh, Pa. under the trademark CR-39. It may also be a rigid plastic element that is combined with a thin glass element to form a laminated lens. Such a lens is described in detail in U.S. Pat. No. 4,793,703 and No. 5,064,712 (Fretz, Jr.).
Currently, organic lenses are produced by filling a cavity with a liquid monomer containing known polymerizing additives. The cavity may be formed by an assembly of two glass mold members held in spaced relationship by a flexible gasket.
The surface contours of the two mold members will be precisely the reverse of the surface contours desired on the organic lens. As a result, the prescription power and surface finish quality of an organic ophthalmic lens rely entirely on the finished accuracy of the glass mold members against which the lens is formed.
Production of the glass mold members is a very specialized, and hence expensive, operation that requires frequent inspections and measurements to achieve the necessary accuracy. Moreover, the polished glass mold members are very prone to damage. Therefore, mold life is quite unpredictable, and may vary from one or two castings to as many as a few hundred. Hence, constant checking of mold surfaces is a necessity, as is maintaining a substantial inventory of mold members for replacement.
The gasketed glass mold approach also entails certain technical disadvantages. A mold release coating must be applied to the glass surfaces, or in the monomer formulation, to avoid adhesion of the cured polymer to the glass. Also, because of a difference in expansion characteristics of the mold materials, leakage of the uncured monomer formulation may occur as the assembly is heated in the early part of a curing cycle.
It is, therefore, a basic purpose of the present invention to provide an improved mold for producing organic polymer, ophthalmic lens elements. The improved mold is inexpensive to produce, and hence disposable. It also provides superior physical properties.